@Shorydouken
So first, I'm going to just say that $600 is pretty low, but I think I can help. On that note, I generally recommend picking up a better PC if possible if for no other reason than you aren't simply getting a console. You're getting something you'll do HW/Work on. You're getting something that will let you learn to code and finally build that kick ass game you've talked about. You're getting a media center. Etc. Further, you can upgrade it. From my original first PC purchase, nothing is the same. I have a fairly high end rig that has been upgraded over 8 years. And when you upgrade, you don't typically have to put in the up front cost of buying a new console. For instance, one year you could just upgrade the GPU. The next you could do the RAM, CPU, and MOBO. So on.
Are you married to a laptop? You'll typically get a little less bang for your buck as laptops being portable is factored into its dollar amount.
Anyway for ~$700,
here is the PCGamer "budget build". Even if that is a little steep, it might be worth looking at. The downside with a build is... that you're going to have to build it. But I recommend this anyway. It allows you to upgrade easier (and cheaper). It gives you more knowledge into what exactly is wrong with your PC. Etc. If you're worried about how difficult it is, it isn't. Most things are idiot-proof these days, and worst case scenario, grab your tech buddy to help out. Anyway, on the budget build, you could cut dollars by getting 500GB HDD. The way Steam works, you don't typically need to have everything installed. I have 1TB, but I only use 500GB on the Windows side... so it is totally doable. Also keep in mind that you'll need to pick up peripherals. You can get a decent flatscreen from Craigs list or a Pawn shop, so the cost can be negligible.
I also found
this site that might help you out. Most of the builds look on the nose, but once you find one you like, I'd ask about it just to be sure. Also, it looks like to save costs you lose memory. For example one has 250GB which isn't terrible for an *only* gaming machine, but otherwise is ass. The same build only has 4GB of memory which is... quickly becoming too little. You won't feel the pinch for a little while, but I'd almost guarantee that you'd upgrade to at least 8GB of RAM before your first year.
As far as pre-builts, I'd double check Newegg and Tigerdirect. Generally, I stay away from big brands (especially Alienware even though their comps are good) because you do pay for that name ie less product for your money. There are pre-built companies like iBuyPower, but you'll want to double check with someone to make sure it is solid. They... sometimes cut corners. My first comp ages ago was iBuyPower and everything was fantastic, except their PSU couldn't support the GPU so random blackouts... yay. In fairness, I bitched and moaned enough that they eventually sent one out that worked fine.
Anyway, hope this helps.